Knife sharpener



FIG. 1 is a front elevation view of a knife sharpener, showing my new design;

FIG. 2 is a rear elevation view thereof;

FIG. 3 is a left side elevation view thereof;

FIG. 4 is a right side elevation view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof;

FIG. 7 is a perspective view thereof; and,

FIG. 8 is a perspective view thereof, shown in the open position.

The broken lines in FIG. 8 depict portions of the knife sharpener that form no part of the claimed design. 

CLAIM The ornamental design for knife sharpener, as shown and described. 